Timing and spatial extent of snow avalanches inferred from tree rings in Şureanu Mountains (Southern Carpathians, Romania)

Snow avalanches (SAs) are one of the debris transfer mechanisms that affect the alpine and subalpine mountain belts. When the avalanches reach the forest, they may disturb the trees. In the last decades, an increasing number of tourists reached the mountain areas worldwide. In remote areas with recreational activities where SA activity is poorly documented, the hazard zonation is hampered by the lack of information about past events. To fill the lack of knowledge regarding SA activity, tree-ring methods might be applied in forested areas to reconstruct extreme past events. This is the case in Şureanu Mountains (Southern Carpathians, Romania), where historical records regarding the past SAs are lacking, but there is a need for hazard zonation mapping on SA-prone slopes attracting winter tourism activities and the infrastructure extent. This study aims to improve the knowledge about the history of SA activity by reconstructing SA events with tree rings in five avalanche paths located on the adjacent slopes of Şureanu Ski Resort. We sampled 219 Norway spruce trees (Picea abies (L.) Karst.) with clear signs of disturbances caused by the past SAs, and their growth anomalies related to the mechanical impact produced by SAs were identified (e.g., scars, tangential rows of traumatic resin ducts, compression wood and growth suppression sequences) and used to reconstruct past SA events. Spatial extent, frequency, and return periods were determined in each of the avalanche path investigated. Tree-ring reconstruction provided an event chronology spanning the period 1975–2018, with calculated return periods ranging between 3 and 10 years. The age of the sampled trees in the study sites limits the period of reconstructed events. In the absence of any SA hazard zoning in Romanian Carpathians in general, and particularly in Şureanu Mountains, the tree-ring reconstructed SA frequencies significantly contribute to a better understanding of SA regimes and further support the SA hazard zoning in the study areas.